Heretofore, optical field enhancement devices, such as sensor devices and Raman spectroscopy devices, which utilize an optical field enhancement effect of a localized plasmon resonance phenomenon on a metal surface have been known. The Raman spectroscopy is a method for obtaining a Raman scattered light spectrum (Raman spectrum) by separating scattered light obtained by projecting single wavelength light onto a substance, and it is used for identifying a substance and the like.
The Raman spectroscopy includes a method called surface-enhanced Raman spectroscopy (SERS) that utilizes an optical field enhanced by localized plasmon resonance in order to enhance weak Raman scattered light (refer to PCT Japanese Publication No. 2006-514286, Japanese Unexamined Patent Publication No. 2012-211839, T. Toda et al., “Enhancement of Positive Hole Injection to Liquid-Crystalline Semiconductor from Au Electrode Surface-Modified by Thiols”, The Journal of the Society of Scientific Photography of Japan, Vol. 70, No. 1, pp. 38-43, 2007, S. Ghadarghadr et al., “Plasmonic array nanoantennas on layered substrates: modeling and radiation characteristics”, Optics Express, Vol. 17, No. 21, pp. 18556-18570, 2009 and T. Pakizeh and M. Kaell, “Unidirectional Ultracompact Optical Nanoantennas”, Nano Letters, Vol. 9, No. 6, pp. 2343-2349, 2009).
This makes use of the principle that if light is projected onto a metal body, in particular, onto a metal body having a nano-order uneven pattern on a surface with a substance being in contact with the surface, optical field enhancement occurs due to localized plasmon resonance and the intensity of Raman scattered light of the sample in contact with the surface of the metal body is enhanced.
More specifically, the surface-enhanced Raman spectroscopy may be implemented using, for example, a substrate having a metal nanostructure on a surface, placing a subject on the metal film of the substrate, and projecting excitation light onto the place where the object is placed.
When measuring a Raman spectrum of a metabolite discharged from a subject of a living body, for example, if the subject is directly placed on the metal film, however, cells may possibly die out by the bactericidal action of silver or the like and the subject may be destroyed. Further, the metabolite discharged from the subject may not sufficiently diffuse and adhere on the metal film hindered by the subject itself placed directly on the metal film, thereby posing a problem that the Raman spectrum of the metabolite cannot be measured with a high degree of accuracy.
In view of the circumstances described above, it is an object of the present invention to provide an optical field enhancement device capable of holding a subject, such as a living body or the like, without destroying cells of the subject and measuring a Raman spectrum of a substance discharged from the subject and the like with a high degree of accuracy. It is a further object of the present invention to provide a light measurement apparatus and method with the use of the optical field enhancement device.
An optical field enhancement device of the present invention includes a transparent substrate having a transparent nanostructure on a surface and a metal film formed on a surface of the nanostructure on the surface of the substrate, and generates an enhanced optical field on a surface of the metal film by an optical field enhancement effect of localized plasmon induced on the surface of the metal film by light projected onto the nanostructure on which the metal film is formed, wherein the device includes a support member for supporting a subject at a position spaced apart from the surface of the metal film.
In the optical field enhancement device of the present invention described above, the support member may be a member that transmits a substance discharged from the subject.
Further, the device may include a liquid holding section for holding a liquid on the metal film.
Still further, the support member may be a member that transmits a metabolite discharged from the subject of a living body.
Further, the support member may be formed of a porous filter.
Still further, the support member may be a member having a plurality of through holes formed therein.
Further, a void may be provided between the support member and the metal film.
Still further, the nanostructure may be made of boehmite.
Further, the metal film may be made of gold or silver.
A light measurement apparatus of the present invention includes the optical field enhancement device described above, a light projection section for projecting excitation light onto the metal film of the optical field enhancement device, and a light detection section for detecting light generated by the projection of the excitation light onto the optical field enhancement device and outputted from the transparent substrate side.
The light measurement apparatus described above may include a scanning mechanism for two-dimensionally scanning the surface of the metal film of the optical field enhancement device with the excitation light.
A light measurement method of the present invention includes the steps of projecting excitation light onto the metal film of the optical field enhancement device described above, and detecting light generated by the projection of the excitation light onto the optical field enhancement device and outputted from the transparent substrate side.
According to the optical field enhancement device of the present invention, a support member is provided in an optical field enhancement device having a transparent substrate with a transparent nanostructure on the surface and a metal film formed on the surface of the nanostructure formed on the surface thereof to support the subject at a position spaced apart from the surface of the metal film. This results in that the subject never contacts with the metal film directly and cells of the subject are prevented from dying out.
Further, if a support member that transmits a substance discharged from the subject is used as the support member, the substance discharged from the subject may reach the metal film by transmitting through the support member, whereby Raman spectrum of the substance near the metal film or the like to be measured with a high degree of accuracy.
Still further, in the optical field enhancement device of the present invention described above, if a liquid holding section for holding a solution is provided on the metal film, the substance discharged from the subject may be diffused sufficiently in the solution and a sufficient amount of the substance may be attached to the metal film.